Use the Process > Enhancements > Adjust Intensity... command to change the brightness, contrast and the Gamma value in the image.
The dialog box that is opened when you use an image processing operation is made up in the same way for every operation. Click here, to switch to a description of this dialog box.
Brightness
Move the Brightness slide control to the right, to make the image brighter. Move the Brightness slide control to the left, to make the image darker.
Contrast
Move the Contrast slide control to change the contrast values of the image.
Values between 50 and 100 increase the image contrast. Values between 0 and 50 decrease the image contrast. At a setting of 50 the image contrast remains unchanged.
Gamma
Move the Gamma slide control to increase the image contrast either in bright image areas or only in dark image areas.
You can find more information on the Gamma correction here.
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